(1) Radioactivity from tagged, blowfly storage protein (calliphorin) injected into "cold" blowfly larvae is subsequently found in several tissues, and diverse proteins, of the adult fly. It is, therefore, "utilized" for adult development. (2) Giant - (or pre-messenger-)RNA is localized exclusively in larval body wall tissue; its synthesis is under hormonal (ecdysone) control, and its occurrence signals the larva's commitment to pupariation. (3) Experiments indicate that an early small peak of larval ecdysone is the biological signal for the cessation of feeding, the commencement of wandering, and gene activation to form giant-RNA. A second, larger "burst" of ecdysone is then required to trigger pupation.